CARACAS, Feb 26 (Reuters) - Pope Francis called on Wednesday for an end to violence in Venezuela that has killed at least 13 people and urged politicians to take the lead in calming the nation's worst unrest in a decade.

Both political camps were demonstrating in cities around the country. In the capital Caracas, female opposition supporters rallied, while agricultural workers marched to the presidential palace in support of the Socialist government.

Students and other opponents of President Nicolas Maduro are demanding that he quit over grievances including high inflation, shocking levels of violent crime, shortages of basic food, and what they say is his repression of political rivals.

The protests are the biggest challenge to Maduro's 10-month-old administration, although there is no sign they could topple him or affect the OPEC nation's oil shipments.

Pope Francis told tens of thousands of people in St. Peter's Square he was "particularly concerned" by recent events.

"I sincerely hope the violence and hostility ends as soon as possible, and that the Venezuelan people, beginning with the responsible politicians and institutions, act to foster national reconciliation through mutual forgiveness and sincere dialogue," Francis said during his weekly address.

Discussions must be based on "truth and justice," he added, and able to tackle "concrete issues for the common good."

Maduro, a 51-year-old former bus driver and union boss, has invited church, business and opposition leaders to a "national peace conference" at the presidential palace on Wednesday.

"Who does dialogue suit more? Nicolas, I think ... This is a government that is becoming extinct, eating itself up."

APPEAL TO MILITARY

Female opposition supporters donned white clothes to march in silence from a western Caracas neighborhood to a nearby National Guard military base, carrying photographs of victims of alleged brutality by the security forces.

"You can disobey illegal orders," they said in an open letter to the troops. "You can refuse a superior if they force you to commit a crime ... don't stain your family's honor."

Meanwhile, pro-Maduro farm workers clad mostly in the bright red of the ruling Socialist Party marched in the center of the capital under the slogan, "Sowing peace and harvesting life!"

"Here are the farmers who are defending the revolution en masse!" said Agricultural Minister Yvan Gil, referring to Maduro's late predecessor Hugo Chavez.

Opposition demonstrations began at the start of the month, but mushroomed when three people were shot dead after a Feb. 12 opposition march in downtown Caracas.

Video and photographs taken on the day showed men widely believed to be state security agents apparently firing pistols at stone-throwing student protesters clashing with police.

On Wednesday, Venezuela's state prosecutor said five members of the national intelligence agency Sebin had been detained over two of the deaths, suspected of crimes including homicide.

Maduro, who narrowly won a presidential vote last April to replace his mentor Chavez, accuses foreign media of working with "imperialists" abroad to project an image of chaos.

TENSE IN TACHIRA

About 150 people have been injured during the two-week crisis, and more than 500 people arrested. The government says the vast majority of them have since been freed pending trial.

Maduro said on Wednesday more than 50 people had died from the unrest. He was referring not only to the 13 people shot or directly killed around protests and rallies, but also those indirectly affected by for example being blocked from hospital.

"An 84-year-old lady died in east Caracas yesterday because they had her held up in a street blockade for more than three hours," he said. "She died in her family's car."

The worst of the trouble is centered on the western state of Tachira, bordering Colombia, where officials in several municipalities reported the looting of a supermarket, clothes shops, discos and other businesses overnight. Several people were hurt by plastic buckshot fired by security forces.

Ricardo Hernandez, mayor of Cardenas municipality, close to the state capital San Cristobal, blamed the looting on hooded motorcyclists, and said he had needed to call on reinforcements from the national police and National Guard troops.

"We won't be intimidated by these delinquents," Hernandez said in a statement. "Take the necessary precautions, such as having telephones close to hand, doors tightly closed ... keep bells or whistles nearby in order to alert the neighbors."

Farmers in Jauregui municipality, a major supplier of vegetables to the rest of the country, said they have 15,000 tonnes of produce that they have not been able to dispatch because of the insecurity and barricaded highways.

Shortages are particularly acute in many areas of Tachira, where blocked roads and the threat of violence mean delivery trucks have not reached stores for days, residents say.

Moderate opposition figures have called for peaceful protests only and voiced despair at the tactics of barricading streets and burning trash in mostly middle-class neighborhoods that are already overwhelmingly pro-opposition.

Venezuelans are approaching a long weekend for Carnival, when families typically head to the beach. Possibly with an eye to taking the heat out of the protests, Maduro extended the break by also declaring Thursday and Friday national holidays. (Additional reporting by Javier Farias and Brian Ellsworth in San Cristobal, Andrew Cawthorne and Deisy Buitrago in Caracas, and Philip Pullella in Vatican City; Editing by Andrew Cawthorne, James Dalgleish and Jan Paschal)

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